Method and system for multi-protocol transmissions

ABSTRACT

Methods and systems for multi-protocol transmissions in shared spectrum are disclosed. According to principles described herein, a wireless transmitter is configured to generate subcarriers or symbol information from one OFDM technology using subcarriers of another OFDM technology. With this approach, a wireless transmitter configured to transmit OFDM symbols using subcarriers and a subcarrier frequency spacing associated with one OFDM protocol can also be configured to transmit OFDM symbols associated with another OFDM protocol which normally uses different subcarriers and a different subcarrier frequency spacing. In one application, an LTE transmitter uses LTE subcarriers to generate 802.11 (e.g. Wi-Fi) subcarrier or symbol information that can be understood by Wi-Fi receivers, for example to reserve the channel for a certain duration, to indicate a transmission time associated with an on-going and/or upcoming symbol transmission or to create a carrier sense indication, for example, to cause Wi-Fi receivers and other radio technologies to consider the channel as busy.

TECHNICAL FIELD

The present disclosure relates to wireless communication systems and inparticular a method and system for multi-protocol transmissions inwireless communication networks.

BACKGROUND

Orthogonal frequency-division multiplexing (OFDM) has become a keyencoding method used by many communications technologies ranging fromwireline to wireless technologies. In fact, OFDM use is pervasive, beingemployed by many technologies including, but not limited to, wiredcommunications such as Digital Subscriber Loop (DSL), Asymmetric DSL(ADSL) and Very-high-bit-rate DSL (VDSL) broadband access technologyover Plain Old Telephone Service (POTS) copper wiring, Digital VideoBroadcasting (DVB), Power Line Communications (PLC), ITU-T G.hn for homewiring LANs, telephone modems, DOCSIS—Data Over Cable System InterfaceSpecification for broadband delivery, MoCA—Multimedia Over Coax Alliancehome networking, and wireless communications including IEEE 802.11 (e.g.Wi-Fi), HIPERLAN, Digital TV, Personal Area Networks (PAN), and UltraWideband Networks (UWB).

OFDM and its multiple access variant OFDMA continue to find increasingapplications, for example in 3^(rd) Generation Partnership Project(3GPP)-based wireless networks such as Long Term Evolution (LTE) andEvolved Universal Mobile Telecommunications System Terrestrial RadioAccess (E-UTRA) networks, but also in IEEE-based networks such as MobileBroadband Wireless Access (MBWA, also referred to as IEEE 802.20). NextGeneration mobile networks are planning to use OFDM as the platform forthis new and exciting product evolution, and even the Wireless GigabitAlliance (WiGig) plans to use OFDM in the 60 GHz frequency band toenable conference room cell sizes to achieve 100 Gigabits per second(Gbps) data rates.

Although these technologies are all based on OFDM, they have significantdifferences in their technology implementations. OFDM is a digitalmodulation technique that uses frequency division multiplexing to createmultiple orthogonal sub-carriers to carry parallel data streams.Sub-carriers are modulated using conventional modulation schemes such asBinary Phase Shift Keying (BPSK) or Quadrature Amplitude Modulation(QAM) with defined symbol rates enabling multiple parallel data streamsto be carried.

The detailed implementations for these various technologies are allquite different, largely driven by channel limitations or restrictions,and desired operational features. For example, 802.11a Wi-Fi employsshort 3.2 microsecond (μs) symbols (with 0.4 or 0.8 μs for the cyclicprefix), and 52 carriers spaced at 312.5 kHz to create a high speed datachannel capable of withstanding the low dispersion experienced in shortreach indoor channels which Wi-Fi APs typically address, while LTEtypically employs longer 66.7 μs symbols (or 71.4 μs with the cyclicprefix) with 15 kHz spaced subcarriers to address significantinter-symbol interference issues typical of long reach outdoor cellularchannels.

Implementations differ by symbol time and sub-carrier spacing, but alsoby many other physical layer parameters including the number ofsub-carriers, channel spacing, Fast Fourier Transform (FFT) size, numberand operation of pilot tones, convolutional codes employed, ForwardError Correction (FEC) design, sub-carrier modulation schemes,time-interleaving, equalizer operation, and Multiple-InputMultiple-Output (MIMO) operation to name a few. Moreover, with theMedium Access Control (MAC) layer defining how the OFDM based physicalmedium is used by higher layer applications, OFDM designs are inherentlycomplex and specific to a particular OFDM technology. As a result, theimplementation of interworking functions with other OFDM basedtechnologies has proven to be very difficult.

Nevertheless, with the explosion of wireless technologies in unlicensedspectrum such as the Unlicensed National Information Interchange (U-NII)bands managed by the Federal Communications Commission (FCC) in theUnited States, there is a desire to see upcoming technologies such asLTE work together to share this spectrum fairly with incumbents such as802.11 (e.g. Wi-Fi) the dominant technology, and provide a positive enduser experience. 3GPP and some to come 5G licensed networks will shortlybegin trials to offer services in unlicensed bands. License AssistedAccess for Long Term Evolution (LAA-LTE or LAA), as the first example,has recently demonstrated cabled operation at Mobile World Congress inMarch of 2015 using the 5 GHz band. Product rollouts are planned in 2016and 2017. However, concerns over interoperability of these differenttechnologies have been raised, driven by expectations of wide scaledeployment of LTE radios into the unlicensed bands.

Since the FCC first made available spectrum in the 5 GHz band for U-NIIoperation in 1997, an etiquette protocol for medium access was developedfor Wi-Fi systems which can be generalized into three rules:

-   -   1. Listen Before Talk (LBT)—Do not use the channel if Radio        Frequency (RF) energy above a threshold is detected,    -   2. Carrier Sense—Do not use the channel if a Wi-Fi carrier        (pilot tones) is detected, and    -   3. NAV Timer—do not use the channel while the Network Allocation        Vector (NAV) timer is counting down to zero.

In Wi-Fi systems, the Clear Channel Assessment (CCA) function employsthese simple etiquette rules to ensure that many Wi-Fi devices can sharethe same unlicensed channel fairly, and avoid transmission collisionswhich may have deleterious effects to both the interferer andinterferee.

With the introduction of new 3GPP-based cellular technologies such asLTE and soon to be 5G into the unlicensed bands, an expanded etiquettewill be required. Wi-Fi, as the main incumbent technology, has a definedetiquette. However, Wi-Fi does not address the complexities andrequirements of 3GPP systems. Although they both use OFDM and bothsupport a number of common features at the physical layer, 3GPP andWi-Fi are fundamentally different.

One of the most fundamental differences is synchronization. Wi-Fioperates asynchronously by applying the etiquette rules andsending/receiving packets when the medium is free. In contrast, 3GPPoperates synchronously and employs advanced scheduling algorithms tomaximize channel utilization, and therefore is not burdened withetiquette rules. As a result, 3GPP is able to carry higher traffic loadsefficiently i.e. in a way that maximizes the use of the valuablefrequency channel resources.

Because of this and other notable differences in OFDM implementation,3GPP-based technologies are not currently designed to support a sharingetiquette, such as that which Wi-Fi supports.

Different possible solutions have been proposed so far claiming to havethe potential for improving fair sharing. One such proposal includesimplementing a power-based LBT detect threshold. With this proposal, theLTE radio would monitor energy on the channel and consider it free ifthe received signal strength indication (e.g. RSSI) is lower than thatthreshold. However, this proposal does not address the variability ofcell sizes due to unlicensed band interference. Also, in someimplementations, the threshold is fairly large (−62 dBm) and limits thecell size. Depending on the channel conditions, there is no guaranteethat the LTE radio will detect a transmitted signal above the thresholdand this ultimately may result in a higher collision count and lowerthroughput.

Other proposals contemplate using a Wi-Fi receiver in the LTE radio tomonitor and detect Wi-Fi pilot tones and/or transport LTE data usingWi-Fi packets. However, these proposals would involve significanthardware and software development and would not be backward compatibleto existing LTE radios currently deployed. Moreover, this proposalcombines transceivers which are fundamentally different to try andcreate a coordinate design. In doing so, it mixes the performance andregulatory aspects of two separate and independent radio transceivers,making the solution extremely complex to design, verify, and havecertified since all of the key design parameters such as power control,AGC, power spectral density, PAR reduction techniques, and PAlinearization techniques such as digital pre-distortion are nowoperating on two separate PHY devices.

Accordingly, to address some or all of the drawbacks noted above, thereis a need for improved method and systems to facilitate co-existence inshared spectrum.

SUMMARY

Methods and systems for multi-protocol transmissions in shared spectrumare disclosed. According to principles described herein, a wirelesstransmitter is configured to generate subcarriers or symbol informationfrom one OFDM technology using subcarriers of another OFDM technology.With this approach, a wireless transmitter configured to transmit OFDMsymbols using subcarriers and a subcarrier frequency spacing associatedwith one OFDM protocol can also be configured to transmit OFDM symbolsassociated with another OFDM protocol which normally uses differentsubcarriers and a different subcarrier frequency spacing.

In one application, an LTE transmitter uses LTE subcarriers to generate802.11 (e.g. Wi-Fi) subcarrier or symbol information that can beunderstood by Wi-Fi receivers, for example to reserve the channel for acertain duration, to indicate a transmission time associated with anon-going and/or upcoming symbol transmission or to create a carriersense indication, for example, to cause Wi-Fi receivers and other radiotechnologies to consider the channel as busy. Depending on the type ofWi-Fi subcarrier or symbol information transmitted, other applicationsare possible.

The embodiments described are primarily in relation to the generation ofWi-Fi subcarriers/symbol information by an LTE transmitter. However, thesame approach is equally applicable to other OFDM technologies such asfor example 802.15 technologies (e.g. ZigBee). Generally, the principlesdescribed herein are applicable to generating subcarriers or symbolinformation from one OFDM technology using subcarriers of another OFDMtechnology. In some embodiments, the principles described herein areapplicable to generate any possible signal to the extent allowed by thespectral bandwidth available to the OFDM transmitter. In addition, theprinciples are equally applicable to other non-OFDM technologies or togenerate non-OFDM signals. For example, the principles described hereinmay be employed to generate IEEE 802.11b CCK signals, using subcarriersor symbol information from one OFDM technology. The principles describedwithin may even be applied to signal generation for applications yetundetermined, a possible example being in-building “radar”, usingspecialized signals to detect and characterize in-building objects forthe purpose of high precision location tracking.

In some implementations, the principles described herein address thespecifics of Wi-Fi systems, and how the carrier sense mechanism operateaddressing the set of carrier functionality necessary to cause a Wi-Fireceiver to determine or indicate the channel as busy. Embodimentsdescribe how Wi-Fi subcarriers/symbol information may be transmittedusing LTE OFDM subcarriers so that the channel may be considered asbusy, both in a preamble type mode (e.g. stand-alone transmission ofWi-Fi preamble or header information) but also as part of a regular LTEtransmission whereby LTE Resource Blocks or symbols are allocated torepresent Wi-Fi pilot tones or symbol information.

In other implementations, the principles described herein extend thediscussion to consider OFDM power level changes which would enable 3GPPLTE systems to present a relatively constant carrier sense to Wi-Fisystems, while carrying user traffic so as to ensure that the LTE datatransmitted over an unlicensed band or channel is not inadvertentlyinterfered with by a Wi-Fi transmitter.

In one broad aspect, there is provided a method for a wireless OFDMtransmitter configured for transmission of a first set of OFDM symbolsusing a base plurality of subcarriers having a base subcarrier frequencyspacing defining a base symbol duration. The method includestransmitting, using the base plurality of subcarriers, a second set ofOFDM symbols during one base symbol duration where each of the secondset of OFDM symbols includes a second Cyclic Prefix (CP) and has asecond symbol duration smaller than the base symbol duration.

In one implementation, the method further includes transmitting, usingthe base plurality of subcarriers, a first set of OFDM symbols whereeach of the first set of OFDM symbols includes a base CP and has a basesymbol duration. In another implementation, the method further includestransmitting, using the base plurality of subcarriers, a third set ofOFDM symbols during one base symbol duration, where each of the thirdset of OFDM symbols includes a third CP and has a third symbol durationsmaller than the base symbol duration.

In yet another implementation, the first set of OFDM symbols includesdata associated with a first OFDM communication protocol and the secondset of OFDM symbols includes data associated with a second OFDMcommunication protocol different from the first OFDM communicationprotocol. In yet another implementation, the first OFDM communicationprotocol comprises an LTE protocol and the second OFDM communicationprotocol comprises an 802.11 protocol.

In yet another implementation, the transmitting of the second set ofOFDM symbols is based on a predetermined OFDM signal in one of a timedomain and a frequency domain where the predetermined ODFM signalcontains data associated with the second OFDM communication protocol. Inyet another implementation, the transmitting of the second set of ODFMsymbols is based on a predetermined set of modulation values for thebase plurality of subcarriers where the predetermined set of modulationvalues correspond to data associated with the second OFDM communicationprotocol.

In yet another implementation, the method further includes generatingfor transmission in the second set of OFDM symbols an OFDM signal in oneof a time domain and a frequency domain where the OFDM signal beinggenerated uses a second plurality of subcarriers different from the baseplurality of subcarriers and where the second plurality of subcarriershas a second subcarrier frequency spacing defining the second symbolduration. In yet another implementation, the OFDM signal generated isassociated with the second OFDM communication protocol and the methodfurther includes interpolating the OFDM signal generated using the baseplurality of subcarriers to produce an OFDM signal to form the secondset of OFDM symbols.

In yet another implementation, the second set of OFDM symbols includescontrol data associated with the second OFDM communication protocolwhere the control data is indicative of one of a transmission length,transmission time, transmission type and a channel reservation timeassociated with at least one of the first and second set of OFDMsymbols. In yet another implementation, the control data comprises oneof Short Training Field (STF) data, Long Training Field (LTF) data,Signal Field (SIG) data. In yet another implementation, the second setof OFDM symbols includes packet data associated with the second OFDMcommunication protocol where the packet data being indicative of one ofa transmission length, transmission time, transmission type and achannel reservation time associated with at least one of first and thesecond set of OFDM symbols. In yet another implementation, the packetdata comprises a Clear To Send (CTS) frame having a timer valueindicative of a transmission end time associated with the at least oneof the first and the second set of OFDM symbols.

In yet another implementation, the first and second sets of OFDM symbolsare transmitted in sequence, as one of contiguous transmissions andnon-contiguous transmissions. In yet another implementation, the firstand second sets of OFDM symbols are transmitted as non-contiguoustransmissions separated by a delay and wherein the second set of OFDMsymbols includes data is indicative of a time for completingtransmission of the first set of OFDM symbols.

In yet another implementation, the second set of OFDM symbols includesan OFDM indication indicative of one of an OFDM type, OFDM mode and anOFDM parameter, a symbol duration, a CP duration, a number ofsubcarriers, a subcarrier spacing, a subcarrier modulation format, and asubcarrier frequency set associated with the first set of OFDM symbols.

In another broad aspect, there is provided an OFDM transmitterconfigured for transmission of a first set of OFDM symbols using a baseplurality of subcarriers having a base subcarrier frequency spacingdefining a base symbol duration. The OFDM transmitter includes circuitrycontaining instructions which, when executed, cause the transmitter toperform any of the method implementations described above.

In yet another broad aspect, there is provided a non-transitory computerreadable memory configured to store executable instructions for an OFDMtransmitter configured for transmission of a first set of OFDM symbolsusing a base plurality of subcarriers having a base subcarrier frequencyspacing defining a base symbol duration. The executable instructionswhen executed by a processor cause the transmitter to perform any of themethod implementations described above.

In yet another broad aspect, there is provided an OFDM transmitting nodeconfigured for transmission of a first set of OFDM symbols using a baseplurality of subcarriers having a base subcarrier frequency spacingdefining a base symbol duration. The OFDM transmitting node includes atransceiver, a processor and a memory containing a transmitting moduleconfigured to transmit, using the base plurality of subcarriers, asecond set of OFDM symbols during one base symbol duration where each ofthe second set of OFDM symbols includes a second Cyclic Prefix (CP) andhas a second symbol duration smaller than the base symbol duration.

In one implementation, the transmitting module is further configured totransmit, using the base plurality of subcarriers, a first set of OFDMsymbols where each of the first set of OFDM symbols includes a first CPand has a first symbol duration equal to the base symbol duration.

In another implementation, the transmitting module is further configuredto transmit, using the base plurality of subcarriers, a third set ofOFDM symbols during one base symbol duration where each of the third setof OFDM symbols includes a third CP and has a third symbol durationsmaller than the base symbol duration.

In yet another implementation, the first set of OFDM symbols includesdata associated with a first OFDM communication protocol and the secondset of OFDM symbols includes data associated with a second OFDMcommunication protocol different from the first OFDM communicationprotocol. In yet another implementation, the first OFDM communicationprotocol is an LTE protocol and the second OFDM communication protocolis an 802.11 protocol.

In yet another implementation, the transmitting module is furtherconfigured to transmit the second set of OFDM symbols based on apredetermined OFDM signal in one of a time domain and a frequencydomain, where the predetermined ODFM signal contains data associatedwith the second OFDM communication protocol. In yet anotherimplementation, the transmitting module is further configured totransmit the second set of ODFM symbols based on a predetermined set ofmodulation values for the base plurality of subcarriers, where thepredetermined set of modulation values corresponds to data associatedwith the second OFDM communication protocol.

In yet another implementation, the memory further includes a generationmodule configured to generate for transmission in the second set of OFDMsymbols a second OFDM protocol signal containing data associated with asecond OFDM protocol in one of a time domain and a frequency domainwhere the second OFDM protocol signal being generated uses a secondplurality of subcarriers different from the base plurality ofsubcarriers, and where the second plurality of subcarriers has a secondsubcarrier frequency spacing defining the second symbol duration. In yetanother implementation, the memory further includes an interpolationmodule configured to interpolate the second OFDM protocol signalgenerated using the base plurality of subcarriers to produce a firstOFDM protocol signal to form the second set of OFDM symbols. In yetanother implementation, the method further includes a signal memorymodule configured to store the first OFDM protocol signal to form thesecond set of OFDM symbols. In yet another implementation, the firstOFDM protocol signal is the predetermined OFDM signal.

In yet another implementation, the memory further includes a switchingmodule configured to determine when data associated with the second OFDMcommunication protocol needs to be transmitted and based on thatdetermination, to route a first OFDM protocol signal containing the dataassociated with the second OFDM communication protocol to thetransmitting module for transmission as the second set of OFDM symbols.In yet another implementation, the first OFDM protocol signal is in oneof a time domain and a frequency domain. In yet another implementationwhere the first OFDM protocol signal is in a frequency domain, theswitching module is configured to route the first OFDM protocol signalto a Inverse Fast Fourier Transform (IFFT) module in the transceiver toperform a first OFDM protocol IFFT function on the first OFDM protocolsignal for transmission as the second set of OFDM symbols via a RadioFrequency (RF) module in the transceiver. In yet another implementationwhere the first OFDM protocol signal is in a time domain, the switchingmodule is configured to route the first OFDM protocol signal to theRadio Frequency (RF) module in the transceiver for transmission as thesecond set of OFDM symbols.

In yet another implementation, the second set of OFDM symbols includescontrol data associated with the first OFDM communication protocol,where the control data is indicative of one of a transmission length,transmission time, transmission type and a channel reservation timeassociated with at least one of the first and second set of OFDMsymbols. In yet another implementation, the control data includes one ofShort Training Field (STF) data, Long Training Field (LTF) data, SignalField (SIG) data. In yet another implementation, the second set of OFDMsymbols includes packet data associated with the second OFDMcommunication protocol, where the packet data is indicative of one of atransmission length, transmission time, transmission type and a channelreservation time associated with at least one of first and the secondset of OFDM symbols. In yet another implementation, the packet dataincludes a Clear To Send (CTS) frame having a timer value indicative ofa transmission end time associated with the at least one of the firstand the second set of OFDM symbols.

In yet another implementation, the first and second sets of OFDM symbolsare transmitted in sequence, as one of contiguous transmissions andnon-contiguous transmissions. In yet another implementation, the firstand second sets of OFDM symbols are transmitted as non-contiguoustransmissions separated by a delay, where the first set of OFDM symbolsincludes data is indicative of a time for completing transmission of thefirst set of OFDM symbols.

In yet another implementation, the second set of OFDM symbols includesan OFDM indication indicative of one of an OFDM type, OFDM mode and anOFDM parameter, a symbol duration, a CP duration, a number ofsubcarriers, a subcarrier spacing, a subcarrier modulation format, and asubcarrier frequency set associated with the first set of OFDM symbols.

Advantageously, the present principles do not require a separate Wi-Fitransmitter as required in existing co-existence proposals. In someimplementations, the Wi-Fi subcarriers/symbol information may begenerated using hardware configured for LTE transmissions and thereforehelp ensure the Wi-Fi transmissions meet requirements imposed on LTEsystems such as, for example, power spectral density, and maximumtransmission power. In other implementations, the interference free cellsize is increased by at least 20 dB, for example from −62 dBm (freechannel threshold) to over −82 dBm which is the sensitivity levelconsidered standard for Wi-Fi systems using 6 Mbps Binary Phase ShiftKeying (BPSK). In yet other embodiments, the cell size is increased by a10 fold factor.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference designators refer to like elements and wherein:

FIG. 1 illustrates one example of a Long Term Evolution (LTE) RadioAccess Network (RAN) and Wireless Local Area Networks (WLANs) configuredto share unlicensed spectrum resources, in accordance with theprinciples described herein;

FIG. 2A-B illustrates an example of LTE subcarriers and Wi-Fisubcarriers used in the LTE RAN and WLANs of FIG. 1, in accordance withthe principles described herein;

FIG. 3 illustrates a timing diagram showing an example of Wi-Fi symbolstransmitted by an LTE node in the LTE RAN of FIG. 1, in accordance withthe principles described herein;

FIG. 4A-B illustrates timing diagram examples of Wi-Fi transmissions byan LTE node in the LTE RAN of FIG. 1 for channel reservation in anunlicensed band in accordance with the principles described herein;

FIG. 5 illustrates a format example for the CTS-To-Self packet of FIG.4A in accordance with the principles described herein;

FIG. 6A-B illustrate format examples for the Wi-Fi header transmissionshown in FIG. 4B in accordance with the principles described herein;

FIG. 7A-B illustrates block diagram examples of the LTE node in the LTERAN of FIG. 1, in accordance with the principles described herein;

FIG. 8 illustrates a block diagram example for the signal generator andtime-domain interpolator in the LTE node of FIG. 7A configured inaccordance with the principles described herein;

FIG. 9 illustrates a block diagram example for the frequency-domaininterpolator in the LTE node of FIG. 7B configured in accordance withthe principles described herein;

FIGS. 10A-10B show a flow chart of example methods for the OFDMtransmitters of FIGS. 7A-B in accordance with the principles describedherein;

FIG. 11 shows a flow chart of another example method for the OFDMtransmitters of FIGS. 7A-B in accordance with the principles describedherein;

FIGS. 12A-12B show a block diagram of exemplary embodiments of OFDMtransmitting and receiving nodes configured in accordance withprinciples described herein, and

FIGS. 13A-13B show a block diagram of other exemplary embodiments ofOFDM transmitting and receiving nodes configured in accordance with theprinciples described herein.

DETAILED DESCRIPTION

The present disclosure is directed to methods and systems formulti-protocol transmissions in shared spectrum. e.g. unlicensed bandsor band normally used for unlicensed access. The principles describedherein are applicable to generating subcarriers or symbol informationassociated with one OFDM technology using another OFDM technology. Thedescription that follows describes how nodes in a first or base OFDMnetwork (e.g. a License Assisted Access (LAA)—Long Term Evolution (LTE)Radio Access Network (RAN)) can transmit subcarrier and/or symbolinformation which can be detected by wireless devices in one or moresecond OFDM network(s) such as for example, a Wireless (e.g. Wi-Fi)Local Area Network (WLAN). However, those having ordinary skill in therelevant art will readily appreciate that the principles describedherein may equally apply to other types of networks.

For example, the first OFDM network may also include other 3^(rd)Generation Partnership Project (3GPP) networks (e.g. Universal MobileTelecommunications System (UMTS), LTE-Advanced (LTE-A)), LTE-Unlicensed(LTE-U), 4^(th) Generation (4G), 5^(th) Generation (5G) or other futuregenerations of a 3GPP communication network infrastructure. Moregenerally, the first OFDM network may include any current or futurewireless network infrastructure configured to generate subcarriers orsymbol information associated with a different OFDM technology, with orwithout a licensed anchor band (so called “standalone” or single carrieraccess network).

Similarly, the second OFDM network(s) described herein primarily asWLANs (e.g. Wi-Fi) may also include other types of 802 networks such asa Wireless Personal Area Networks (WPAN) or a Wireless Metropolitan AreaNetworks (WMAN). However, the second OFDM network(s) may also includewireless networks that use a different OFDM technology such as forexample 802.15 networks (e.g. ZigBee). More generally, the secondwireless network(s) may include any OFDM network that uses a subcarrierspacing equal to or greater than the subcarrier spacing used in thefirst OFDM network. This is intended to include OFDM networks which arevariations of the OFDM technology used in the first OFDM network butwith a greater subcarrier spacing (e.g. a second LTE network with asubcarrier spacing greater than the carrier spacing of a first LTEnetwork). For clarity and as used herein, the term WLAN or Wi-Fi is usedto cover all of these possibilities for the second OFDM network(s).

Referring now to FIG. 1, there is shown one example of an LAA-LTE RAN 10(an example of the first OFDM network) in which an access node 60 isconfigured to transmit subcarrier and/or symbol information which can bedetected by wireless devices 50, 52, 54, 56, 58 operating in WLANs 20,30 (examples of a second OFDM network). As is conventional for LAAoperation, the unlicensed band is used to operate a (secondary) carrierto add capacity to a (primary) carrier operating in licensed spectrum(e.g. an LTE carrier). Operation of the primary licensed carrier may beunder the control of the access node 60 or another node in the LAA-LTERAN 10.

The access node 60 is an eNodeB but in other implementations, the accessnode 60 may be a Node B (NB), evolved Node B (eNB), base station, basestation controller (BSC), radio network controller (RNC), relay, donornode controlling relay, base transceiver station (BTS), transmissionpoint, transmission node, remote RF unit (RRU), remote radio head (RRH),a node in a distributed antenna system (DAS), or a memory managementunit (MMU). Generally, the access node 60 is configured to controltransmissions to or from UEs in the LTE RAN 10 but other nodes in theLTE RAN 10, a Core Network (CN) 70 or in a network outside of a RAN/CNinfrastructure (e.g. an Internet Protocol (IP) node in an IP network)may be configured for that purpose. In other implementations, a wirelessdevice or UE (for example, a relay node UE) may be configured totransmit subcarrier and/or symbol information which can be detected bydevices that use a different OFDM technology (e.g. devices in the WLANs20, 30). It is to be understood that the functionality described hereinin relation to nodes that are configured to transmit such subcarrier orsymbol information in a wireless network may also equally apply towireless devices (e.g. UEs) configured as such.

In FIG. 1, the access node 60 provides wireless devices within itscoverage (e.g. devices 40, 50) with access to network services in onemore core networks 70, in this example, an Evolved Packet Core (EPC)network which includes a Mobility Management Entity 74 and a Packet DataNetwork (PDN) Gateway (PGW) 72. Each wireless device 40, 50 isconfigured for wireless communication in the LAA-LTE RAN 10 (e.g. as aUser Equipment (UE) and may be of any type, including, for example awireless terminal (also known as a mobile station, a mobile phone(“cellular” phone), a desktop, laptop, netbook, and/or tablet computer,a laptop embedded equipment (LEE), laptop mounted equipment (LME), or aportable device such as an e-book reader, watch, digital music and/orvideo player, camera, game controller and/or device but also may be acomputing-like device such as a heart monitoring implant, biochiptransponder, automobile, sensor, modem, thermostat, and/or other home orcar appliance generally referred to as an Internet of Things (IoT)device, a machine type communication (MTC) device (also known as amachine-to-machine (M2M) or device-to-device (D2D) device.

In the example of FIG. 1, the LAA-LTE RAN 10 shares the unlicensed bandwith WLANs 20, 30 for transmissions involving at least some of thewireless devices in its coverage (e.g. wireless device 50). Generally,the WLANs 20, 30 may each include any number of wireless devicescommunicating directly or via an Access Point (AP) with other devices inthe same or different networks. In the example of FIG. 1, WLAN 20 isshown to include WLAN devices 52, 54, AP 58 as well as wireless device50 while WLAN 30 includes WLAN devices 54 and 56. Other networkconfigurations for WLANs 20, 30 or other types of networks or deviceswhich may share unlicensed spectrum resources with device 50 in theLAA-LTE RAN 10 are possible.

As is conventional, devices 50, 52, 54 and AP 58 in WLAN 20 and devices54, 56 in WLAN 30 (herein generically referred to as WLAN or Wi-Fidevices) are configured to share a band of spectrum using some form ofmedia access method and/or transmissions based on contention. As iswell-known, there are many examples of such contention-based approaches.Examples include Listen-Before-Talk (LBT), Carrier Sense Multiple Access(CSMA)—with Collision Detection (CSMA-CD), CSMA with Collision Avoidance(CSMA-CA), etc. Using a contention-based method, a WLAN device 50, 52,54, 56, 58 will try to determine whether another transmission is inprogress in the channel or band used. This determination may be based onthe detection of a carrier wave, signal or energy in the channel ofinterest. If a carrier or energy is detected in the channel of interest(in another fully or partially overlapping channel), the WLAN device 50,52, 54, waits for the transmission in progress to finish beforeinitiating its own transmission.

In the example of FIG. 1, the LAA-LTE RAN 10 may include wirelessdevices 40 in a location outside the coverage of WLANs 20, 30, and withwhich spectrum resources are not shared. As a result, the wirelessdevices 40, 50 described in the embodiments herein may (but do not needto) be configured for operation on multiple different wireless networks.In the example of FIG. 1, wireless device 50 is configured as adual-mode device (i.e. configured as a UE for operation in the LAA-LTERAN 10 as well as a WLAN device for operation in WLANs 20, 30) whilewireless device 40 is configured as a UE for operation in the LAA-LTERAN 10 only. For clarify, the principles of the present disclosure applywhether or not wireless devices 40, 50 in the LAA-LTE RAN 10 areconfigured as single-mode or multi-mode devices.

3GPP systems such as the LAA-LTE RAN 10 of FIG. 1 typically operateoutdoors, usually from high powered macros cell sites designed to coverranges up to several kilometers. The resulting coherence bandwidth ofthe channel is very small as the delay spread (i.e. the impulse responseof the channel) can be quite large due to distant reflections frombuilding and other environmental factors. To address this issue, 3GPPsystems break the available bandwidth into many narrower sub-carriers orsub-channels and transmit the data in parallel streams. FIG. 2A shows atime-frequency diagram 80 of a set of LTE sub-channels (only a subsetshown) used in a channel of the LTE RAN 10 of FIG. 1. The LTEsub-channels are 15 KHz wide and correspond to a set of LTE sub-carriersL-SC_(1-M), typically 1200 (M=1200) for a 20 MHz channel. In thatexample, each LTE subcarrier L-SC_(1-M) is modulated using varyinglevels of QAM modulation, e.g. QPSK, QAM, 64QAM or possibly higherorders depending on signal quality. Each OFDM symbol 82 is therefore alinear combination of the instantaneous signals on each of thesub-carriers L-SC_(1-M) in the channel. Because data is transmitted inparallel rather than serially, LTE symbols 82 are generally much longerthan symbols on single carrier systems of equivalent data rate. In theexample of FIG. 2A, each LTE symbol 82 is 66.7 microseconds (μs) longand is preceded by a 4.7 μs cyclic prefix (CP) (not shown), which isused to reduce Inter-symbol Interference (ISI). The total symbol length(including the CP) is 71.4 μs.

In contrast, Wi-Fi systems operate (mostly) indoors, usually from lowpower APs designed to cover ranges up to 50 or 100 meters. The resultingcoherence bandwidth of the channel is large, as the delay spread (e.g.the impulse response of the channel) is usually very short, typicallyless than 500 nanoseconds (ns). As a result, Wi-Fi systems use wider312.5 KHz sub-channels. FIG. 2B shows a time-frequency diagram 90 of aset of Wi-Fi sub-channels (only a subset shown) used in a channel of theWLANs 20, 30 of FIG. 1. The Wi-Fi sub-channels correspond to a set ofWi-Fi sub-carriers W-SC_(1-N), typically 52 (N=52) in a 20 MHz channel,which are spaced apart by 312.5 kHz. Because of the larger sub-channelspacing, Wi-Fi symbols 84 are generally much shorter than LTE symbols82. In the example of FIG. 2A, each Wi-Fi symbol 82 is 3.2 μs long andis preceded by a 0.8 μs cyclic prefix (CP) (not shown) for a totalduration of 4 μs.

Understanding the differences in, for example the number of carriers,the carrier spacing and the symbol time duration, it is possible for onebase OFDM system (denoted as OFDM1) configured to transmit informationusing its defined set of (base) subcarriers to also be configured toencode subcarrier or symbol information of another OFDM system (denotedas OFDM2) in a way that such information can be decoded by receiversconfigured in accordance with that other system. In someimplementations, the subcarrier spacing Δf₁, symbol duration T₁=k₁/Δf₁and system bandwidth BW₁ of the OFDM1 system and those of the OFDM2system (Δf₂, T₂=k₂/Δf₂, and BW₂) are such that:

Δf ₁ <Δf ₂  (1)

T ₁ >T ₂  (2)

BW₁=(M*Δf ₁)≧BW₂=(N*Δf ₂)  (3)

where

k₁ and k₂ are integer values, which are typically set to 1,

M is the number of OFDM1 subcarriers, and

N is the number of OFDM2 subcarriers.

In other implementations, an OFDM1 transmitter is configured to generateand transmit subcarrier and/or symbol information of any OFDM2 systemthat uses a subcarrier spacing larger (or substantially larger, e.g. bya factor of 10 or 20) than the OFDM1 subcarrier spacing. Stated anotherway, the OFDM1 transmitter is configured to generate and transmitsubcarrier and/or symbol information of any OFDM2 system that uses asymbol duration smaller (or substantially smaller, e.g. by a factor of10 or 20) than the OFDM1 symbol duration. In yet other implementations,the OFDM1 transmitter is configured to generate and transmit subcarrierand/or symbol information of any OFDM2 system that has a systembandwidth that is smaller or equal to the LTE system bandwidth. Intypical LTE and Wi-Fi systems for example, the LTE subcarrier spacing issmaller than the Wi-Fi subcarrier spacing (which means the Wi-Fi symbolduration is smaller than the LTE symbol duration) and the Wi-Fi systembandwidth is smaller than the LTE system bandwidth. As such, it ispossible for an LTE transmitter to encode and transmit Wi-Fi informationas a set of Wi-Fi symbols that can be recovered by a Wi-Fi receiver. Insome implementations, in addition to being configured to generate andtransmit Wi-Fi and LTE symbols, the LTE transmitter may also beconfigured to generate subcarrier and/or symbol information of anotherOFDM technology.

In other implementations, an LTE transmitter (e.g. the access node 60 ofFIG. 1) can use LTE subcarriers L-SC_(1-M) to generate 802.11 (e.g.Wi-Fi) subcarrier or symbol information that can be understood by Wi-Fireceivers, for example to reserve the channel for a certain duration, toindicate a transmission time associated with an on-going and/or upcomingsymbol transmission or to create a carrier sense indication, forexample, to cause Wi-Fi receivers and other radio technologies toconsider the channel as busy. The embodiments described below areprimarily in relation to the generation of Wi-Fi subcarriers/symbolinformation in an LTE transmitter. However, it is understood that thesame approach is equally applicable to other OFDM technologies such asfor example 802.15 technologies (e.g. ZigBee). Generally, the principlesdescribed herein are applicable to generating subcarriers or symbolinformation from one OFDM technology using another OFDM technology.

FIG. 3 illustrates a timing diagram 100 showing an example of a symboltransmission by an LTE transmitting node (e.g. the access node 60 in theLTE RAN 10 of FIG. 1), in accordance with the principles describedherein. In this example, the access node 60 is configured to transmitWi-Fi information, for example Wi-Fi header and/or packet data toindicate its current use of a (unlicensed) channel shared with devicesin the WLANs 20, 30 and/or to reserve the channel for a certain amountof time (further details below). The Wi-Fi information is modulated bythe access node 60 in the form of a set of one or more Wi-Fi symbols110, 112, 114 (only three shown) and transmitted during the duration ofone LTE symbol 102 (e.g. 66.7 μs). In order to be properly decoded bydevices in WLANs 20, 30, each Wi-Fi symbol 110, 112, 114 includes arespective CP 110 a, 112 a, 114 a (e.g. 0.8 μs) and has a symbolduration (e.g. 3.2 μs) that conforms to the duration expected by devicesin the WLANs 20, 30. In the example of FIG. 3, the number of Wi-Fisymbols 110, 112, 114 is designed to fit into one LTE symbol duration102 (e.g. after an LTE symbol preamble or CP 102 a) but in otherimplementations, the number of Wi-Fi symbols 110, 112, 114 issubstantially less than one LTE symbol duration 102. In yet otherimplementations, the access node 60 uses up to sixteen Wi-Fi symbols110, 112, 114 in a 66.7 μs LTE symbol time duration. In yet otherimplementations, the access node 60 uses some of the Wi-Fi symbols 110,112, 114 for Wi-Fi header data and the rest for Wi-Fi packet or framedata, the size of which depends on the Wi-Fi modulation rate used. Inyet other implementations, the Wi-Fi symbols 110, 112, 114 are organizedin multiple sets to span over multiple LTE symbol durations where eachset is configured to fit in the duration of one LTE symbol. In yet otherimplementations, the first Wi-Fi symbol set is preceded by an LTE CP(e.g. CP 102 a), but subsequent Wi-Fi symbol sets are transmittedwithout an LTE CP to ensure proper recovery by Wi-Fi receivers.

In the example of FIG. 3, the Wi-Fi transmission is followed byconventional LTE symbols 104 (only one shown) which can be decoded andreceived by conventional LTE receivers (e.g. UEs 40, 50). In someimplementations, the Wi-Fi information contained in the Wi-Fi symbols110, 112, 114 and intended for devices in the WLANs 20, 30 is indicativeof a transmission time, length, type associated with and/or a channelreservation time necessary for transmitting the Wi-Fi symbols 110, 112,114, the LTE symbols 104 or a combination of both. Advantageously, withthis approach, the access node 60 can generate a Wi-Fi header or evenone or more complete Wi-Fi packets.

In some implementations, the access node 60 generates Wi-Fi symbols 110,112, 114 to contain a Wi-Fi header or a Clear-To Send (CTS) packet suchas a “CTS-to-Self” packet to reserve the channel with a “virtual carriersense”, enabling devices in the WLANs 20, 30 to receive thisheader/packet information down to −82 dBm or lower and refrain fromtransmitting until after the LTE transmission (e.g. the LTE symbols 104)has been sent. Moreover, in some implementations, by generating andtransmitting both the Wi-Fi symbols 110, 112, 114 and the LTEtransmission 104, the access node 60 can apply the same (LTE) processingfunctions such as filtering, PAR, digital pre-distortion, PSDmanagement, RMS power control, etc., to the generation and transmissionof both the Wi-Fi symbols 110, 112, 114 and the LTE transmission 104which follows.

It is important to note that different Wi-Fi header and/or packet datamay be used for different applications. In one implementation forexample, the access node 60 may use Wi-Fi symbols 110, 112, 114 to sendPROBE REQUEST packets to detect nearby Wi-Fi APs. In anotherimplementation, the access node 60 uses the Wi-Fi symbols 110, 112, 114to send disassociation or de-authentication packets to Wi-Fi Stations(clients) in an attempt to move them to the LTE RAN 10. Using theprinciples described herein, the access node 60 can use to Wi-Fi symbols110, 112, 114 to send other types of Wi-Fi packets or frames includingfor example NULL packets, Wi-Fi sounding packets, LWA packets, PointCoordination Function (PCF) beacons, etc.

FIGS. 4A-B show timing diagram examples of two different Wi-Fitransmissions 124, 134 the access node 60 can use to reserve the channelfor a subsequent LTE symbol transmission (shown as Transmission TimeIntervals (TTIs) 126 a-d, 138 a-d). Each of these Wi-Fi transmissions124, 134 has a duration that fits within one LTE symbol but as notedabove, the Wi-Fi transmissions 124, 138 may span multiple LTE symbols inother implementations. In the example of FIG. 4A, a Wi-Fi CTS-to-Selfpacket 124 is used to reserve the channel for transmitting a set of LTETTIs 126 a-d (only four shown) while in the example of FIG. 4B, a Wi-Fiheader 134 is used for TTIs 138 a-d.

According to principles of the present disclosure, each of theCTS-To-Self packet 124 and header 134 contains a channel reservationindication indicating an amount of time during which the access node 60intends to use the channel. In some implementations, the reservationindication prevents listening devices (e.g. devices in the WLANs 20, 30that have received and demodulated the indication) to perform anytransmission until the reservation time has expired.

As described below in more detail, there are many possibilities for thechannel reservation indication. In the example of FIG. 4A, the channelreservation indication is a Network Allocation Vector (NAV) indicationin the CTS-To-Self packet 124. In some implementations, the NAVindication is a NAV timer value defining how long the channel will bereserved. In some implementations, the NAV timer value is indicative ofa time required to transmit the CTS packet, the LTE TTIs 126 a-d (e.g.NAV reservation time 128) and/or a combination thereof. In otherimplementations, the NAV timer value is an end time of the LTE TTI 126a-d transmission. The devices that receive and demodulate the CTS packetwill refrain from transmitting until a timer set to the NAV timer valueexpires. In yet other implementations, the channel reservationindication is included in a different field of the CTS-to-Self packet124. Generally, any packet data or any field of a Wi-Fi packet may beused for the channel reservation indication. In other implementations,the channel reservation indication is a value indicative of any one of atransmission length, time or type or a channel reservation timeassociated with the CTS-to-Self packet 124, the LTE symbols and/or both.Other possibilities exist for the channel reservation indication.

In the example of FIG. 4B, the channel reservation indication is alength reservation indication or other control data in the Wi-Fi header134 representing an octet count associated with the LTE TTIs 138 a-d. Inother implementations, the length reservation indication (or controldata) is a time duration required for transmitting the Wi-Fi header 134,the LTE TTIs 138 a-d (e.g. length reservation time 140) and/or acombination thereof. In yet other implementations, the lengthreservation indication is an end time of the LTE TTI 138 a-dtransmission. In yet other implementations, the Wi-Fi header 134 and theLTE TTIs 138 a-d may be viewed as a combined packet transmission 130where the LTE TTIs 138 a-d (and possibly other information) form thepacket data payload with a length that corresponds to the lengthreservation indication. In those implementations, Wi-Fi receivers (e.g.devices in WLANs 20, 30) recover the Wi-Fi header 134 and refrain fromusing the channel until the packet data payload (e.g. the LTE TTIs 138a-d) has been completely transmitted while LTE receivers (e.g. theaccess node 60) are configured to receive and demodulate only the LTETTIs 138 a-d (the Wi-Fi header may be unrecoverable).

Depending on the nature of the channel reservation indication used, theWi-Fi and LTE transmissions are either contiguous or non-contiguoustransmissions. For example, the access node 60 may, in someimplementations, initiate the LTE transmission immediately aftercompleting the Wi-Fi transmission or alternatively, wait after a certaindelay (e.g. as in FIG. 4A). In other implementations such as the exampleshown in FIG. 4B, the access node 60 transmits noise (or some RF power)during that delay to maintain the transmit power envelope and preventWi-Fi devices to assume the channel is free.

In some implementations, the access node 60 may continue to use thechannel beyond the time duration or end time indicated by the channelreservation indication. For example, the access node 60 may also beconfigured for an additional transmission following TTIs 126 a-d or TTIs138 a-d. The additional transmission may be an additional set of LTETTIs or some other transmission (e.g. a Wi-Fi transmission) and iscontiguous with the preceding TTIs 126 a-d, 138 a-d to prevent Wi-Fidevices from transmitting during the additional transmission. In thoseimplementations, the channel reservation indication indicates how longthe channel is reserved for the LTE TTIs 126 a-d, 138 a-d but not forthe additional transmission.

In some implementations, the access node 60 performs a channelavailability check using a contention-based method, for exampleListen-Before-Talk (LBT) 122, 132 to determine whether anothertransmission is in progress in the channel or band used. Thisdetermination may be based on the detection of a carrier wave, signal orenergy in the channel or band of interest (e.g. with a −62 dBmthreshold). If during that time, a carrier or energy is detected in theband or channel of interest (in another fully or partially overlappingchannel or band), the access node 60 waits for the transmission inprogress to finish before initiating its own transmission.Alternatively, if no carrier or energy is detected, the access node 60(immediately) transmits either the CTS-To-Self packet 124 or headerinformation 134 and completes the subsequent LTE transmission (TTIs 126a-d or 138 a-d).

FIG. 5 illustrates an example of a Physical Layer Convergence Protocol(PLCP) Protocol Data Unit (PPDU) 150 that includes the CTS-To-Selfpacket 124 shown in FIG. 4A in accordance with the principles describedherein. In this example, the CTS-to-Self packet, denoted as 170, isincluded in a PLCP Service Data Unit field 156 of the PPDU 150 whichalso includes a preamble 152 and a header 154 (collectively hereinreferred to as header) as well as tail and pad fields 158, 160. The CTSframe 170 includes a frame control field 172 that specifies the type offrame 170 (in this case a CTS-To-Self frame), a duration field 174 tospecify a NAV timer value, a Receiver Address (RA) field 176 which isset to the Transmitter Address for a CTS-To-Self packet and a FrameCheck Sequence (FCS) field 178 which specifies an error-correcting codefor the CTS packet 170. In some implementations, eleven Wi-Fi symbols,each 4 μs in duration, are required to transmit the CTS-To-Self packet170 (as included in a PPDU 150) for a total transmission length of 44 μswhich fits into a 71.4 or 80 μs LTE symbol.

FIG. 6A illustrates an example of a format for the Wi-Fi header 134shown in FIG. 4B in accordance with the principles described herein. Inthis example, the Wi-Fi header 134 is a PLCP header 208 which includes apreamble 202 and a Signal field (SIG) 204 (collectively herein referredto as header data) contains a channel reservation indication (in the SIG204) to reserve the channel for a certain period of time. The channelreservation indication is set in a length field 214 as an octet countwhich is indicative of the amount of data to follow in a data field 206.Together with a modulation rate for the data specified in rate field210, the channel reservation indication in the length field 214 isindicative of the time required to transmit or an end transmission timefor the data (e.g. up to 5 msec). The data contained in the data field206 and the PLCP header 208 are shown as a combined transmission 200where the data field length corresponds to the channel reservationindication contained in the SIG 204. However the PLCP header 208 and thedata field 206 may be sent as two separate transmissions (e.g.non-contiguous transmissions). In some implementations, the dataincludes LTE symbols (e.g. LTE TTIs 138 a-d in FIG. 4B) but in otherexamples, the data may include additional or other information such asWi-Fi symbols and/or a random transmission (e.g. noise 136). Otherpossibilities exist for the data in the data field 206. As noted above,the data in the data field 206 may also be followed by an additionaltransmission, such as an additional set of LTE TTIs or some othertransmission (e.g. a Wi-Fi transmission).

In addition to the length field 214, the SIG 204 also includes the ratefield 210 that specifies a modulation rate for the data in the datafield 206, a reserved field 212, a parity field 216, a tail field 218and a service field 220. In some implementations, the tail field 218 isset to a value indicative of a type of symbols or OFDM associated withthe data in the data field 206 (e.g. in this case an LTE type). In otherimplementations, the tail field 218 is set of a first value when LTEsymbols are present in the data field 206 and a different value whennon-LTE symbols (e.g. Wi-Fi symbols) are included). Advantageously, insome implementations, setting the tail field 218 to a value indicativeof the presence of LTE symbols in the data field 206 notifies listeningdevices (devices configured to receive and demodulate the PLCP header208) that the data field 206 contains symbols of a different OFDM type(e.g. LTE symbols). In other implementations, this indication is an OFDMindication and may be included in another field (other than the tailfield 218 or the SIG 204) at the same or different layer. For example,in yet other implementations, the OFDM indication is included in a MAClayer protocol field, such as the Frame Control Field which containsbits (e.g. b0 and b1) normally used to specify an associated protocol.This OFDM indication may represent an OFDM type or mode or an OFDMparameter associated with the data in the data field 206 such as symbolduration, CP duration, number of subcarriers, subcarrier spacing,subcarrier modulation formats, subcarrier frequencies, etc.

FIG. 6B shows other format examples for the Wi-Fi header 134 shown inFIG. 4B that can be used by the access node 60 to reserve a channelaccording to the principles described herein. For a legacy mode,transmission 240 includes a Legacy (L) Short Training Field (STF) 242, aLegacy (L) Long Training Field (LTF) field 244, and a Legacy (L)-SIG 246that contains a channel reservation indication to reserve the channelfor the data (e.g. LTE symbols or Wi-Fi symbols) to be transmitted indata field 248. For a mixed mode, transmission 250 includes an L-STF252, an L-LTF 254, an L-SIG 256, a High Throughput (HT)-SIG field 258,an HT-STF 260, an HT-LTF 262 and a data field 264. Either the L-SIG 246or the HT-SIG 258 is configured to contain a channel reservationindication to reserve the channel for the data to be transmitted in thedata field 264. For a green field mode, transmission 270 includes anL-STF 272, an HT SIG 274, an HT-STF 276, an HT-LTF 278 and a data field280. The HT-SIG 274 is configured to contain a channel reservationindication to reserve the channel for the data to be transmitted in thedata field 280. In some implementations, the data in the data field 248,264, 280 includes LTE symbols (e.g. LTE TTIs 138 a-d in FIG. 4B) but inother examples, the data may include additional or other informationsuch as Wi-Fi symbols and/or a random transmission (e.g. noise 136).Other possibilities exist for the data in the data field 248, 264, 280.As noted above, the data in the data field 248, 264, 280 may also befollowed by an additional transmission, such as an additional set of LTETTIs or some other transmission (e.g. a Wi-Fi transmission).

Although the examples provided above show that the channel reservationindication used is a length value included in a SIG field, otherpossibilities exist. Generally, any control data or field in the Wi-Fiheader 134 can be used for the channel reservation indication. In otherimplementations, the channel reservation indication is a valueindicative of any one of a transmission length, time or type or achannel reservation time associated with the Wi-Fi header 134, the datain the data field LTE symbols and/or both. Other possibilities exist forthe channel reservation indication.

According to principles of the present disclosure, there are manydifferent ways for an LTE transmitter (the access node 60) to generateWi-Fi symbols containing Wi-Fi header or packet data. In one example,the LTE transmitter is configured to obtain a dynamically generated(i.e. generated when needed) or a pre-determined time-domain signal orvector of M samples (e.g. a Common Public Radio Interface (CPRI) I/Qvector) that spans over a portion or an entire LTE symbol duration. Inanother implementation, the LTE transmitter is configured to obtain adynamically generated or a pre-determined frequency-domain vector of MLTE subcarrier modulation values for one LTE symbol. These M subcarriermodulation values may be QAM constellations, or subcarriers I/Q values.In some implementations, when the M subcarrier modulation vector isapplied in the LTE transmitter to an M-point Inverse Fast FourierTransform (IFFT), the resulting Wi-Fi transmission generated can berecovered at Wi-Fi receivers by an N-point FFT. The Wi-Fi transmissionmay also be recovered by other LTE receivers since the transmissionwould align with LTE subcarrier constellations.

There are many different configurations that can be used in an LTEtransmitter to generate Wi-Fi subcarriers or symbol information. In oneexample, the LTE transmitter configuration may include two separate andindependent physical layers (LTE and Wi-Fi), with different ASICcomponents and/or circuitry that reflect differences in for example, thesymbol durations, cyclic prefix durations, number of subcarriers,subcarrier spacing, subcarrier modulation formats, subcarrierfrequencies, or any one of numerous MAC layer differences, but it doesnot preclude that a common ASIC or other hardware circuitry can beconfigured to support both OFDM technologies. However, in otherimplementations, it is possible to integrate both OFDM technologies intothe same device or set of components and configure these components tooperate either in an LTE or Wi-Fi mode. The transmitter configurationexamples provided below apply to equally to implementations withdedicated circuitry or common to all OFDM technologies supported (andoperable in different modes).

Turning now to FIGS. 7A and 7B, there is shown two different blockdiagram examples of a base OFDM transmitter 300, 350 of a (base) OFDMtechnology, denoted as OFDM1 (e.g. a 3GPP or LTE technology), which, inaddition to being configured for OFDM1 transmissions, is also configuredto transmit subcarrier or symbol information of another OFDM technology,denoted as OFDM2 (e.g. a Wi-Fi technology), such that it can be decodedby OFDM2 receivers (e.g. Wi-Fi receivers). The OFDM1 transmitters 300,350 (e.g. the access node 60 in the LTE RAN 10 of FIG. 1) are eachconfigured to provide and transmit a set of OFDM2 symbols (i.e. one ormore) during one OFDM1 symbol duration. In some implementations, each ofthe OFDM2 symbols includes an OFDM2 Cyclic Prefix (CP) and has an OFDM2symbol duration that is smaller than the OFDM1 symbol duration. In someimplementations, after transmitting the OFDM2 symbol set, the OFDM1transmitter 300, 350 is configured to transmit a set of OFDM1 symbols,using the base OFDM1 subcarriers. The OFDM2 and OFDM1 symbol settransmissions may be contiguous or non-contiguous. As mentioned above,the ODFM1 transmitter 300, 350 may use the OFDM2 symbol set to encodevarious types of OFDM2 related information for various purposes,including for example to reserve a channel for a certain duration, toindicate a transmission time associated with the OFDM2 and/or OFDM1symbol set transmission or to create a carrier sense indication, forexample, to cause OFDM2 receivers to consider the channel as busy. Insome implementations, the OFDM2 symbol set includes Wi-Fi header dataand/or Wi-Fi packet data and the OFDM1 symbol set includes LTE data (orLTE TTIs) and the Wi-Fi header or packet data in the OFDM2 symbol set isindicative of a transmission length, a transmission time, a transmissiontype and/or a channel reservation time associated with the Wi-Fiheader/packet data, the LTE data or a combination of both.

The OFDM1 transmitter 300 has an OFDM1 transmission chain 302, an OFDM1Inverse Fast Fourier Transform (IFFT) unit 304 and an OFDM1 RF unit 306(e.g. DAC, mixer, and PA) which, in combination, are configured forOFDM1 transmissions via one or more antennas 307. In someimplementations the OFDM1 transmission chain 302 converts a serial OFDM1symbol stream of Binary Phase Shift Keying (BPSK) or QuadratureAmplitude Modulation (QAM) data into M parallel streams. The OFDM1transmission chain output is modulated onto M base OFDM1 subcarriers viathe OFDM1 IFFT unit 304 and then transmitted via the RF unit 306 andantennas 307.

According to principles of the present disclosure, the OFDM1 transmitter300 also includes circuitry that is configured to produce an OFDM1signal that carries OFDM2 information for transmission via the antennas307. In one implementation, the circuitry includes an OFDM2 signalgenerator 312 configured to generate an OFDM2 signal. The OFDM2 signalis a time-domain signal that contains predetermined or defined OFDM2symbol information generated with, for example, N OFDM2 subcarriers. Inthat implementation, the circuitry further includes an OFDM2-OFDM1Time-Domain (TD) interpolator 314 that interpolates in the time-domainthe OFDM2 signal generated (further details below) to produce afrequency-domain OFDM1 signal denoted as FDS that is fed into the OFDM1IFFT and RF units 304, 306 via switch 308 for transmission via antenna307.

However other possibilities exist. In another implementation, thecircuitry includes an OFDM1 signal memory 316 where the FDS signal isstored. When the OFDM1 transmitter 300 determines that OFDM2 informationneeds to be transmitted, it generates the FDS dynamically (e.g. on thefly) using the signal generator 312 and TD interpolator 314 or simplyreads the FDS signal from the signal memory 316 and routes it into theOFDM1 IFFT and RF units 304, 306 via switch 308. In implementationswhere the FDS signal is read from the signal memory 316, the circuitrymay only include signal memory 316. In other implementations, the storedFDS signal is a predetermined or defined vector of OFDM1(frequency-domain) subcarrier modulation values (e.g. a vector with Mvalues) that includes values representative of predetermined or definedOFDM2 information.

In one example, the following vector of non-zero LTE subcarriermodulation values can be used by an LTE transmitter to produce an STFusing a group of 2048 subcarriers (sequentially numbered from −1024 to1024):

STF_LTE_SCs=[−499,−415,−332,−249,−165,−82,85,168,252,335,418,502]

STF_LTE_SC_Value=√(13/6)*[1+i,−1−i,1+i,−1−i,−1−i,1+i,−1−i,−1−i,1+i,1+i,1+i,1+i]

Each of the twelve LTE subcarriers identified above in the STF_LTE_SCsarray by sequence number is set to a corresponding non-zero modulationvalue in the STF_LTE_SC_Value array. All other LTE subcarriers in thegroup (those not identified in the STF_LTE_SCs array) are set to a zerovalue (e.g. (0+0i)).

In another example, for an LTE transmitter configured to use 2048subcarriers, the following vector of LTE subcarrier modulation valuescan be used to produce an LTF:

LTF_LTE_SCs=[−540,−519,499,−478,−457,−436,−415,−394,−374,−353,−332,−311,−290,−269,−249,−228,−207,−186,−165,−144,−124,−103,−82,−61,−40,−19,22,43,64,85,106,127,147,168,189,210,231,252,272,293,314,335,356,377,397,418,439,460,481,502,522,543]

LTF_LTE_SC_Value=[1,1,−1,−1,1,1,−1,1,−1,1,1,1,1,1,1,−1,−1,1,1,−1,1,1,1,1,1,1,1,−1,−1,1,1,−1,1,−1,1,−1,−1,−1,−1,−1,1,1,−1,−1,1,−1,1,−1,1,1,1,1];

Each of the fifty-two LTE subcarriers identified above in theLTF_LTE_SCs array by sequence number is set to a corresponding non-zeromodulation value in the LTF_LTE_SC_Value array while all other LTEsubcarriers in the group (those not identified in the LTF_LTE_SCs array)are set to a zero value (e.g. (0+0i).

Other possibilities exist for the LTE subcarrier modulation values.

In yet another implementation, the TD interpolator 314 instead uses atime-domain OFDM1 signal TDS to carry the OFDM2 information. In thatimplementation, when the OFDM1 transmitter 300 determines that the OFDM2information needs to be transmitted, the OFDM1 transmitter 300 routesthe TDS signal into the OFDM1 RF unit 306 via switch 310 directly fromthe TD interpolator 314 or via the signal memory 316. In implementationswhere the TDS signal is read from the signal memory 366, the circuitrymay only include signal memory 366. In other implementations, the storedTDS signal is a predetermined or defined vector of OFDM1 (time-domain)samples (e.g. a vector with M samples) that is representative ofpredetermined or defined OFDM2 information.

In some implementations, the switch 308 (or 310 depending on whether theTD interpolator 314 produces a TDS or FDS signal) is part of a switchingmodule that is configured to determine when OFDM2 information needs tobe transmitted and based on that determination, to route the FDS (orTDS) signal containing the OFDM2 information to the OFMD1 IFFT 304 (orOFDM1 RF 306) for transmission as a set of OFDM2 symbols or route theOFDM1 transmission chain output for transmission as a set of OFDM1symbols.

In other implementations, the switching module (or switch 308, 310)controls whether OFDM2 or OFDM1 information is transmitted via the OFDM1IFFT 304 and/or RF 306. For example, when the switching moduledetermines that OFDM2 information needs to be transmitted (e.g. when aWi-Fi preamble or CTS packet needs to be sent to reserve the channel fora subsequent LTE transmission), the switching module routes the FDSsignal (or TDS signal) containing the OFDM2 information to the OFDM1IFFT 304 (or OFDM1 RF 306) for transmission as a set of OFDM2 symbols.Conversely, when the switching module determines that OFDM1 informationneeds to be transmitted (e.g. the subsequent LTE transmission), theswitching module instead routes the output of the OFDM1 transmissionchain 302 containing the OFDM1 information to the OFDM1 IFFT 304 fortransmission via the OFDM1 RF 306 as a set of OFDM1 symbols.

In some implementations, prior to determining that OFDM2 informationneeds to be transmitted, a channel availability check is performed first(e.g. by a receiver in communication with the OFDM1 transmitter 300) todetermine whether the transmission channel or band used is free. Thischeck may be based on whether a carrier wave, signal or energy can bedetected in the channel or band of interest (e.g. with a −62 dBmthreshold). If no carrier or energy is detected, the switching moduleroutes the switching module routes the FDS signal (or TDS signal)containing the OFDM2 information to the OFDM1 IFFT 304 (or OFDM1 RF 306)for transmission as a set of OFDM2 symbols. In some implementations, theswitching module may rely on a channel availability indication providedby a channel availability unit (not shown) before it can determine thatOFDM2 information can be transmitted.

In some implementations, it may be desirable for the OFDM1 transmitter300 to occupy the channel as soon as possible after the channelavailability check to ensure that other receivers do not consider thechannel as free before the OFDM1 transmitter had a chance to begin itsown OFDM2 transmission. In implementations where a delay is inevitable(for example when the OFDM2 information needs to be generated,interpolated, stored and/or converted into the time domain via the OFDM1IFFT 304), the OFDM1 transceiver 300 may be configured to transmit atime domain signal that can be fed directly into the OFDM1 RF unit 306until the desired OFDM2 information becomes available for transmission.For example, if the desired OFDM2 information is in the form of afrequency domain signal (FDS) that needs to go through the OFDM1 IFFT304 (e.g. after having being generated in the OFDM2 signal generator 312and processed in the interpolator 314 and/or the signal memory 316), theswitching module may be configured, when it receives a positive channelavailability indication, to route a repeatable time domain signaldirectly into the RF unit 306 until the desired OFDM2 information isready for transmission. In some implementations, the repeatable timedomain signal is another OFDM2 signal which has a repetitive or cyclicalpattern. In one example, the repeatable OFDM2 signal is a sequence ofLTFs and/or STFs. Other possibilities exist for the repeatable timedomain signal used prior to transmitting the desired OFDM2 information.

FIG. 8 shows a block diagram example of a configuration for the OFDM2signal generator 312 and OFDM2-OFDM1 TD interpolator 314 of FIG. 7A togenerate and interpolate a Wi-Fi signal into an LTE signal in the timedomain, in accordance to principles described herein. In this example, aWi-Fi signal generator 402 includes a 64 point Wi-Fi IFFT unit 406 thatis configured to perform an IFFT for each symbol time duration of afrequency-domain Wi-Fi signal 404 carrying pre-determined or definedWi-Fi information (e.g. a Wi-Fi header or packet). The Wi-Fi signalgenerator 402 also includes a CP unit 408 that is configured to add a CPto each Wi-Fi symbol generated to create a set of Wi-Fi symbols carryingthe pre-determined Wi-Fi information.

The Wi-Fi symbol set is fed into a LTE time-domain interpolator 412 thatincludes a re-sampling unit 414 configured to resample (e.g. bytime-domain interpolation or low pass filtering) the Wi-Fi symbol set toproduce a time-domain LTE signal 420 (e.g. C-PRI I/Q data). The LTEtime-domain interpolator 412 may, in some implementations, include apadding unit 416 to pad the LTE signal 420 to turn it into an LTE I/Qvector (e.g. the TDS signal of FIG. 7A) that can be processed byconventional LTE RF circuitry (e.g. the OFDM1 RF unit 306 of FIG. 7A).In other implementations, the LTE time-domain interpolator 412 mayfurther include an LTE FFT unit 418 to obtain a corresponding LTE signal422 in the frequency-domain (e.g. the FDS signal of FIG. 7A) that can beprocessed by conventional LTE IFFT circuitry (e.g. the OFDM1 IFFT unit304 of FIG. 7A). In yet other implementations, the LTE FFT unit 418 hasan input size equal to the total size of the Wi-Fi symbols in the Wi-Fisymbol set and an output equal to the number of LTE subcarriers (e.g.2048). Alternatively, the LTE FFT unit 418 used is the same as that usedin a conventional LTE receiving chain. Other implementations arepossible.

Returning to FIG. 7B, there is shown a different OFDM1 transmitterconfiguration which can be used if frequency-domain interpolation ispreferred. Similarly to the OFDM1 transmitter 300, OFDM1 transmitter 350also has an OFDM1 transmission chain 352, an OFDM1 IFFT unit 354, aswitch 358 (or 360), an OFDM1 RF unit 356, antenna(s) 357, and circuitryincluding an OFDM2 signal generator 362, OFDM2-OFDM1 interpolator 364and/or an OFDM1 signal memory 366. In contrast however, the OFDM2-OFDM1interpolator 364 interpolates in the frequency domain the OFDM2 signalgenerated (further details below) to produce either a frequency-domainOFDM1 signal FDS carrying the OFDM2 information that can be transmittedby the OFDM1 RF unit 356 via switch 358 and OFDM1 IFFT unit 354 or atime-domain OFDM1 signal TDS that can be transmitted directly by theOFDM1 RF unit 356 via switch 360.

In some implementations, the switch 358 (or 360 depending on whether theFD interpolator 364 produces an FDS or TDS signal) is part of aswitching module that is configured to determine when OFDM2 informationneeds to be transmitted and, based on that determination, to route theFDS (or TDS) signal containing the OFDM2 information to the OFMD1 IFFT354 (or OFDM1 RF 367) for transmission as a set of OFDM2 symbols orroute the OFDM1 transmission chain 352 output for transmission as a setof OFDM1 symbols. Similarly to the example shown in FIG. 7A, the FDS (orTDS) signal transmitted may be read from the OFDM1 signal memory 366 asthe stored output of the FD interpolator 364 or as a predeterminedvector of OFDM1 frequency domain (or time domain) subcarrier modulationvalues (or samples) representative of the OFDM2 information.

Similarly to the OFDM1 transmitter 300, the switching module in theOFDM1 transmitter 350 controls whether OFDM2 or OFDM1 information istransmitted via the OFDM1 IFFT 354 and/or RF 356. For example, when theswitching module determines that OFDM2 information needs to betransmitted (e.g. when a Wi-Fi preamble or CTS packet needs to be sentto reserve the channel for a subsequent LTE transmission), the switchingmodule routes the FDS signal (or TDS signal) containing the OFDM2information to the OFDM1 IFFT 354 (or OFDM1 RF 356) for transmission asa set of OFDM2 symbols. Conversely, when the switching module determinesthat OFDM1 information needs to be transmitted (e.g. the subsequent LTEtransmission), the switching module instead routes the output of theOFDM1 transmission chain 352 containing the OFDM1 information to theOFDM1 IFFT 354 for transmission via the OFDM1 RF 356 as a set of OFDM1symbols.

In some implementations, prior to determining that OFDM2 informationneeds to be transmitted, a channel availability check is performed first(e.g. by a receiver in communication with the OFDM1 transmitter 350)based on whether a carrier wave, signal or energy can be detected in thechannel or band of interest (e.g. with a −62 dBm threshold). If nocarrier or energy is detected, the switching module routes the switchingmodule routes the FDS signal (or TDS signal) containing the OFDM2information to the OFDM1 IFFT 354 (or OFDM1 RF 356) for transmission asa set of OFDM2 symbols. In some implementations, the switching modulemay rely on a channel availability indication provided by a channelavailability unit (not shown) before it can determine that OFDM2information can be transmitted.

In some implementations, it may be desirable for the OFDM1 transmitter350 to occupy the channel as soon as possible after the channelavailability check to ensure that other receivers do not consider thechannel as free before the OFDM1 transmitter had a chance to begin itsown OFDM2 transmission. In some implementations, the OFDM1 transceiver350 may be configured to transmit a time domain signal that can be feddirectly into the OFDM1 RF unit 356 until the desired OFDM2 informationbecomes available for transmission. For example, if the desired OFDM2information is in the form of a frequency domain signal (FDS) that needsto go through the OFDM1 IFFT 354 (e.g. after having being generated inthe OFDM2 signal generator 362 and processed in the interpolator 364and/or the signal memory 366), the switching module may be configured(when it receives a positive channel availability indication) to route arepeatable time domain signal (e.g. a sequence of LTFs and/or STFs) tothe OFDM1 RF unit 56 so that it can be transmitted until the desiredOFDM2 information is ready for transmission. Other possibilities existfor the repeatable time domain signal used prior to transmitting thedesired OFDM2 information.

FIG. 9 shows a block diagram example of a configuration for the OFDM2OFDM2-OFDM1 FD interpolator 364 of FIG. 7B configured to interpolate, inthe frequency domain, a Wi-Fi signal 456 carrying pre-determined ordefined Wi-Fi information (e.g. a Wi-Fi header or packet) into an LTEsignal 470, 472. In this example, a Frequency Domain (FD) interpolationunit 452 includes a symbol interpolator 458 that interpolates on a Wi-Fisymbol-by-symbol basis i.e. one Wi-Fi symbol at a time. In oneimplementation, the symbol interpolator 458 interpolates the N (e.g. 64)Wi-Fi subcarriers into M (e.g. 2048) LTE subcarriers using the following“sinc” function:

${{LTE\_ Subcarrier}(m)} = {{\sum\limits_{n = {- 32}}^{32}{Wi}} - {{Fi\_ subcarrier}(n) \times \sin \; {c( \lfloor {m - {( \frac{312.5}{15} )n}} \rfloor )}}}$     m = −1024, …  , 1024

where:

${\sin \; {c(x)}} = \frac{\sin \; \pi \; x}{\pi \; x}$

However, this is only one function example for the symbol interpolator458. Other frequency interpolation functions may be used to map N Wi-Fisubcarriers into M LTE subcarriers.

The symbol interpolator 458 takes as input the Wi-Fi signal 456 in thefrequency domain that corresponds to one Wi-Fi symbol time duration. Theoutput is fed into an LTE IFFT unit 460 which produces a set of Mtime-domain samples (e.g. 2048) which span over one LTE symbol duration.In some implementations, the time-domain set of M samples is truncatedin truncation unit 464 (e.g. by selecting a subset of samples (e.g. 98)to correspond to one Wi-Fi symbol duration (e.g. 3.2 μs) therebyproducing LTE I/Q data corresponding to the one Wi-Fi symbol durationprocessed by the symbol interpolator 458. The FD interpolation unit 452also includes a concatenation unit 464 that concatenates the LTE I/Qdata produced with any LTE I/Q data that might have been produced forWi-Fi symbols previously processed by the interpolator 452. The Wi-Fisymbols are thus processed in the FD interpolation unit 452 until all ofthe Wi-Fi symbols in the Wi-Fi signal have been processed. Theconcatenation unit 464 produces a time-domain LTE signal or I/Q vector470 (e.g. the TDS signal of FIG. 7B) formed of the concatenated LTE I/Qdata corresponding to the entire Wi-Fi signal) so that it can then beprocessed by conventional LTE RF circuitry (e.g. the OFDM1 RF unit 356of FIG. 7B). The FD interpolating unit 452 may, in some implementations,include an LTE FFT unit 468 to obtain a corresponding LTE signal 472 inthe frequency-domain (e.g. the FDS signal of FIG. 7B) that can beprocessed by conventional LTE IFFT circuitry (e.g. the OFDM1 IFFT unit354 of FIG. 7B). Alternatively, the LTE FFT unit 468 is the same as thatused in a conventional LTE receiving chain. Other implementations arepossible.

FIG. 10A shows an example method 600 for the OFDM transmitter 300 ofFIG. 7A. In this method, the OFDM transmitter 300 is assumed to beconfigured for first OFDM symbol transmissions using a base plurality ofsubcarriers M₁ having a base subcarrier frequency spacing Δf₁ defining abase symbol duration T₁. At step 602, the method 600 includes obtaininga time domain representation TD₂ of a plurality of second OFDM symbols,each of the plurality of second OFDM symbols being associated with asecond plurality of subcarriers N₂ having a second subcarrier frequencyspacing Δf₂<Δf₁ and a second symbol duration T₂>T₁. At step 604, themethod includes interpolating TD₂ to generate an M₁ point time domainrepresentation TD₁, and at step 606, the method includes transmitting afirst OFDM symbol transmission based on the time domain representationTD₁ generated.

In some implementations, the method 600 includes, performing an M₁ pointFast Fourier Transform (FFT) of TD₁ to generate a frequency domainrepresentation FD₁ of TD₁, and performing an M₁ point Inverse FFT (IFFT)to generate the first OFDM symbol transmission. In otherimplementations, each of the plurality of second OFDM symbols isrepresented in TD₂ by N₂ points where N₂ is smaller than M₁. In otherimplementations, the interpolating of TD₂ includes resampling TD₂ toobtain M₁ points for the time domain representation TD₁. In yet otherimplementations, the obtaining includes generating TD₂ using an N₂ pointInverse FFT (IFFT). In other implementations, the obtaining includesreading TD₂ from a memory.

In some implementations, M₁ is a number of LTE subcarriers and N₂ is anumber of Wi-Fi subcarriers. In other implementations, M₁=2048, Δf₁=15KHz, T₁=66.7 us, N₂=64, Δf₂=312.5 KHz and T₂=3.2 us. Otherimplementations are possible.

FIG. 10B shows an example method 700 for the OFDM transmitter 350 ofFIG. 7B. In this method, the OFDM transmitter 350 is assumed to beconfigured for first OFDM symbol transmissions using a base plurality ofsubcarriers M₁ having a base subcarrier frequency spacing Δf₁ defining abase symbol duration T₁. The method 700 includes a set of steps 702,704, 706, 708 which are performed for each one of a plurality of secondOFDM symbols associated with a second plurality of subcarriers N₂ havinga second subcarrier frequency spacing Δf₂>f₁ and a second symbolduration T₂<T₁. First, the method 700 includes interpolating at step 702a frequency domain representation FD₂ of the one second OFDM symbol togenerate an M₁ point frequency domain representation FD₁ of FD₂. At step704, the method 700 then includes performing an Inverse Fast FourierTransform (IFFT) of FD₁ to generate an M₁ point time domainrepresentation TD₁ of the one second OFDM symbol, and truncating TD₁ atstep 706 to a symbol duration equal to the second symbol duration. Themethod 700 further includes at step 708 concatenating the TD₁ truncatedwith any previously concatenated TD₁ to produce a concatenated timedomain representation CTD₁. If at step 710, steps 702-708 were performedfor the last of the plurality of second OFDM symbols, the method 700goes to step 712 where it includes transmitting a first OFDM symboltransmission based on the concatenated time domain representation CTD₁.Otherwise, the method 700 goes back and performs steps 702-708 for thenext second OFDM symbol until all of the second OFDM symbols have beenprocessed.

In some implementations, the method further includes performing an M₁point Fast Fourier Transform (FFT) of the CTD₁ to generate a frequencydomain representation FD₁ of CTD₁ and performing an M₁ point IFFT togenerate the first OFDM symbol transmission representative of theplurality of second OFDM symbols.

In some implementations, the interpolating of FD₂ is performed inaccordance with the following function:

${{Base\_ Subcarrier}(m)} = {\sum\limits_{n = {- 32}}^{32}{{Second\_ Subcarrier}(n) \times {{sinc}( \lfloor {m - {( \frac{312.5}{15} )n}} \rfloor )}}}$     m = −1024, …  , 1024

where:

${\sin \; {c(x)}} = \frac{\sin \; \pi \; x}{\pi \; x}$

In some implementations, M₁ is a number of LTE subcarriers and N₂ is anumber of Wi-Fi subcarriers. In other implementations, M₁=2048, Δf₁=15KHz, T₁=66.7 μs, N₂=64, Δf₂=312.5 KHz and/or T₂=3.2 us. Otherimplementations are possible.

Simulation tests have shown that OFDM2 symbols (e.g. Wi-Fi symbols)generated based on the principles described above can be received anddemodulated by an OFDM2 receiver (e.g. Wi-Fi) despite the fact that theyhave been generated by an OFDM1 transmitter (e.g. LTE) with OFDM1subcarriers. In some implementations, an OFDM2 receiver is configured toreceive, using N OFDM2 subcarriers, a set of OFDM2 symbols generatedwith M OFDM1 subcarriers. In other implementations, the OFDM2 receiverincludes an N-point FFT to receive the OFDM2 symbol set which wasgenerated with an M-point IFFT in the OFDM1 transmitter. Otherpossibilities exist for the OFDM2 receiver. In yet otherimplementations, the OFDM2 symbol set includes OFDM2 control or packetdata which is indicative of one of a transmission length, transmissiontime, transmission type and a channel reservation time associated withthe OFDM2 symbol set, an OFDM1 symbol set transmitted after the OFDM2symbol set or a combination thereof. Other possibilities exist for theOFDM2 receiver.

FIG. 11 shows a flow chart of another example method 800 for the OFDMtransmitters 300, 350 of FIGS. 7A-B in accordance with the principlesdescribed herein. In this method, the OFDM transmitters 300, 350 areassumed to be configured for transmission of a first set of OFDM symbolsusing a base plurality of subcarriers having a base subcarrier frequencyspacing defining a base symbol duration. At step 802, the method 800includes transmitting, using the base plurality of subcarriers, a secondset of OFDM symbols during one base symbol duration, each of the secondset of OFDM symbols including a second CP and having a second symbolduration smaller than the base symbol duration. Optionally at step 804,the method 800 may also include transmitting, using the base pluralityof subcarriers, a first set of OFDM symbols, each of the first set ofOFDM symbols including a base CP and having a base symbol duration. Themethod may also include optionally at step 806 transmitting, using thebase plurality of subcarriers, a third set of OFDM symbols during onebase symbol duration, each of the third set of OFDM symbols including athird CP and having a third symbol duration smaller than the base symbolduration.

FIGS. 12A-B are block diagrams of exemplary embodiments of respectivelya (base) OFDM1 transmitting node 1000 (e.g. an LTE transmitter) and anOFDM2 receiving node (e.g. a Wi-Fi receiver) configured to transmit orreceive OFDM2 symbols generated using base OFDM1 subcarriers inaccordance with the principles of the present disclosure.

As illustrated in FIG. 12A, OFDM1 transmitting node 1000 includes atransceiver 1002, one or more processor(s) 1004, memory 1006 whichincludes one or more of a generation module 1008, an interpolationmodule 1010, a signal memory module 1012 a switching module 1014 and atransmitting module 1016. In one embodiment, the transceiver 1002 may bereplaced by a transmitter and a receiver (not shown). The generationmodule 1008 is configured to perform the signal generation functionalitydescribed above which includes generating a (time-domain or frequencydomain) OFDM2 signal that contains pre-determined or defined OFDM2information. The interpolation module 1010 is configured to perform theinterpolation functionality described above, which includesinterpolating the OFDM2 signal to produce a (time-domain or frequencydomain) OFDM1 signal representative of predetermined or defined OFDM2information. The signal memory module 1012 is configured to perform thestoring functionality described above which includes storing the OFDM1signal generated or a predetermined OFDM1 signal that contains the OFDM2information. The switching module 1014 is configured to perform theswitching functionality described above, which includes routing theOFDM1 signal containing the OFDM2 information for transmission as a setof OFDM2 symbols or routing the output of an OFDM1 transmission chainfor transmission as a set of OFDM1 symbols. The transmitting module 1016is configured to perform the transmitting functions described abovewhich includes transmitting using an OFDM1 plurality of subcarriers, aset of OFDM2 symbols during one OFDM1 symbol duration and transmittingusing the OFDM1 plurality of subcarriers, a set of OFDM1 symbols, eachof an OFDM1 symbol duration.

Depending on the implementation (e.g whether the OFDM2 information isgenerated on the fly or retrieved from memory when needed), not all ofthe generation, interpolation, storing and/or switching functions needto be performed as noted above and as such, some of these modules may beoptional. For example, in one implementation, the OFDM2 information isstored in the signal memory module 1012 in advance, and the memory 1006only includes the signal memory module 1012, the switching module 1014and the transmitting module 1016 respectively performing the functionsdescribed above. The generation module 1008, interpolation module 1010,signal memory module 1012, switching module and transmitting module 1016are implemented at least partially in the memory 1006 in the form ofsoftware or (computer-implemented) instructions executed by theprocessor(s) 1004 within the OFDM1 transmitting node 1000 or distributedacross two or more nodes (e.g., the OFDM1 transmitting node 1000 andanother node). In another example, the processor(s) 1004 includes one ormore hardware components (e.g., Application Specific Integrated Circuits(ASICs)) that provide some or all of the generation, interpolation,storing, switching and transmitting functionality described above. Inanother embodiment, the processor(s) 1004 include one or more hardwarecomponents (e.g., Central Processing Units (CPUs)), and some or all ofthe generation, interpolation, storing, switching and transmittingfunctionality described above is implemented in software stored in,e.g., the memory 1006 and executed by the processor 1004. In yet anotherembodiment, the processor(s) 1004 and memory 1006 form processing means(not shown) configured to perform the generation, interpolation,storing, switching and transmitting functionality described above.

As illustrated in FIG. 12B, OFDM2 receiving node 1100 includes atransceiver 1102, one or more processor(s) 1104, and memory 1106 whichincludes a receiving module 1108, and a transmission control module1110. In one embodiment, the transceiver 1102 may be replaced by atransmitter and a receiver (not shown). The receiving module 1108 isconfigured to perform the receiving functionality described above which,as noted above includes receiving a set of OFDM2 symbols transmittedfrom an OFDM1 transmitting unit, using OFDM1 subcarriers. Thetransmission control module 1110 is configured to perform thetransmission control functionality described above, which includesdetermining if the OFDM2 symbols contain data indicative of one of atransmission length, a transmission time, a transmission type, and/or achannel reservation time associated with at least one of the OFDM2symbol set and a set of OFDM1 symbols to be transmitted by the OFDM1transmitting unit and if so, refraining from transmitting based on thedata received.

The receiving module 1108 and transmission control module 1110 areimplemented at least partially in the memory 1106 in the form ofsoftware or (computer-implemented) instructions executed by theprocessor(s) 1104 within the OFDM2 receiving node 1100 or distributedacross two or more nodes (e.g., the OFDM2 receiving node 1100 andanother node or device). In another example, the processor(s) 1104includes one or more hardware components (e.g., Application SpecificIntegrated Circuits (ASICs)) that provide some or all of the receivingand transmission control functionality described above. In anotherembodiment, the processor(s) 1104 include one or more hardwarecomponents (e.g., Central Processing Units (CPUs)), and some or all ofthe receiving and transmission control functionality described above isimplemented in software stored in, e.g., the memory 1106 and executed bythe processor 1104. In yet another embodiment, the processor(s) 1104 andmemory 1106 form processing means (not shown) configured to perform thereceiving and transmissions control functionality described above.

FIGS. 13A-B show a variant for each of the OFDM transmitting andreceiving node examples of FIGS. 12A-B, denoted respectively as OFDMtransmitting node 1200, and ODFM receiving node 1300. Each of the nodes,1200, 1300 includes a transceiver 1202, 1302 and circuitry containing(computer-implemented) instructions which when executed by one or moreprocessor(s) 11204, 1304 cause their respective node 1200, 1300 toperform some or all of the generation, interpolation, storing,switching, transmitting, receiving and transmission controlfunctionality described above. In yet another variant, the circuitryincludes the respective memory 1206, 1306 and processor(s) 1204, 1304which, similarly to the example nodes 1000 and 1100 of FIGS. 12A-B maybe implemented in many different ways. In one example, the memories1206, 1306 contain instructions which, when executed, cause therespective node 1200, 1300 to perform some or all of their generation,interpolation, storing, switching, transmitting, receiving andtransmission control functionality described above. Otherimplementations are possible.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope of thepresent disclosure.

1. A method for a wireless OFDM transmitter configured for transmissionof a first set of OFDM symbols using a base plurality of subcarriershaving a base subcarrier frequency spacing defining a base symbolduration, the method comprising transmitting, using the base pluralityof subcarriers, a second set of OFDM symbols during one base symbolduration, each of the second set of OFDM symbols including a secondCyclic Prefix (CP) and having a second symbol duration smaller than thebase symbol duration.
 2. The method of claim 1 further comprisingtransmitting, using the base plurality of subcarriers, a first set ofOFDM symbols, each of the first set of OFDM symbols including a base CPand having a base symbol duration.
 3. The method of claim 1 furthercomprising transmitting, using the base plurality of subcarriers, athird set of OFDM symbols during one base symbol duration, each of thethird set of OFDM symbols including a third CP and having a third symbolduration smaller than the base symbol duration.
 4. The method of claim 2wherein the first set of OFDM symbols comprises data associated with afirst OFDM communication protocol and the second set of OFDM symbolscomprises data associated with a second OFDM communication protocoldifferent from the first OFDM communication protocol.
 5. The method ofclaim 4 wherein the first OFDM communication protocol comprises an LTEprotocol and the second OFDM communication protocol comprises an 802.11protocol.
 6. The method of claim 4 wherein the transmitting of thesecond set of OFDM symbols is based on a predetermined OFDM signal inone of a time domain and a frequency domain, the predetermined ODFMsignal containing data associated with the second OFDM communicationprotocol.
 7. The method of claim 4 wherein the transmitting of thesecond set of ODFM symbols is based on a predetermined set of modulationvalues for the base plurality of subcarriers, the predetermined set ofmodulation values corresponding to data associated with the second OFDMcommunication protocol.
 8. The method of claim 1 further comprisinggenerating for transmission in the second set of OFDM symbols an OFDMsignal in one of a time domain and a frequency domain, the OFDM signalbeing generated using a second plurality of subcarriers different fromthe base plurality of subcarriers, the second plurality of subcarriershaving a second subcarrier frequency spacing defining the second symbolduration.
 9. The method of claim 8 wherein the OFDM signal generated isassociated with the second OFDM communication protocol, the methodfurther comprising interpolating the OFDM signal generated using thebase plurality of subcarriers to produce an OFDM signal to form thesecond set of OFDM symbols.
 10. The method of claim 4 wherein the secondset of OFDM symbols comprises control data associated with the secondOFDM communication protocol, the control data being indicative of one ofa transmission length, transmission time, transmission type and achannel reservation time associated with at least one of the first andsecond set of OFDM symbols.
 11. The method of claim 10 wherein thecontrol data comprises one of Short Training Field (STF) data, LongTraining Field (LTF) data, Signal Field (SIG) data.
 12. The method ofclaim 4 wherein the second set of OFDM symbols comprises packet dataassociated with the second OFDM communication protocol, the packet databeing indicative of one of a transmission length, transmission time,transmission type and a channel reservation time associated with atleast one of first and the second set of OFDM symbols.
 13. The method ofclaim 12 wherein the packet data comprises a Clear To Send (CTS) framehaving a timer value indicative of a transmission end time associatedwith the at least one of the first and the second set of OFDM symbols.14. The method of claim 2 wherein the first and second sets of OFDMsymbols are transmitted in sequence, as one of contiguous transmissionsand non-contiguous transmissions.
 15. The method of claim 14 wherein thefirst and second sets of OFDM symbols are transmitted as non-contiguoustransmissions separated by a delay and wherein the second set of OFDMsymbols comprises data is indicative of a time for completingtransmission of the first set of OFDM symbols.
 16. The method of claim 4wherein the second set of OFDM symbols comprises an OFDM indicationindicative of one of an OFDM type, OFDM mode and an OFDM parameter, asymbol duration, a CP duration, a number of subcarriers, a subcarrierspacing, a subcarrier modulation format, and a subcarrier frequency setassociated with the first set of OFDM symbols.
 17. A OFDM transmitterconfigured for transmission of a first set of OFDM symbols using a baseplurality of subcarriers having a base subcarrier frequency spacingdefining a base symbol duration, the OFDM transmitter comprisingcircuitry containing instructions which, when executed, cause thetransmitter to transmit, using the base plurality of subcarriers, asecond set of OFDM symbols during one base symbol duration, each of thesecond set of OFDM symbols, including a second Cyclic Prefix (CP) andhaving a second symbol duration smaller than the base symbol duration.18. The OFDM transmitter of claim 17 wherein the instructions arefurther configured to cause the transmitter to transmit, using the baseplurality of subcarriers, a first set of OFDM symbols, each of the firstset of OFDM symbols including a first CP and having a first symbolduration equal to the base symbol duration.
 19. The OFDM transmitter ofclaim 17 wherein the instructions are further configured to cause thetransmitter to transmit, using the base plurality of subcarriers, athird set of OFDM symbols during one base symbol duration, each of thethird set of OFDM symbols including a third CP and having a third symbolduration smaller than the base symbol duration.
 20. The OFDM transmitterof claim 18 wherein the first set of OFDM symbols comprises dataassociated with a first OFDM communication protocol and the second setof OFDM symbols comprises data associated with a second OFDMcommunication protocol different from the first OFDM communicationprotocol.
 21. The OFDM transmitter of claim 18 wherein the first OFDMcommunication protocol is an LTE protocol and the second OFDMcommunication protocol is an 802.11 protocol.
 22. The OFDM transmitterof claim 20 wherein the instructions are configured to cause thetransmitter to transmit the second set of OFDM symbols based on apredetermined OFDM signal in one of a time domain and a frequencydomain, the predetermined ODFM signal containing data associated withthe second OFDM communication protocol.
 23. The OFDM transmitter ofclaim 20 wherein the instructions are configured to cause thetransmitter to transmit the second set of ODFM symbols based on apredetermined set of modulation values for the base plurality ofsubcarriers, the predetermined set of modulation values corresponding todata associated with the second OFDM communication protocol.
 24. TheOFDM transmitter of claim 17 wherein the instructions are furtherconfigured to cause the transmitter to generate for transmission in thesecond set of OFDM symbols an OFDM signal in one of a time domain and afrequency domain, the OFDM signal being generated using a secondplurality of subcarriers different from the base plurality ofsubcarriers, the second plurality of subcarriers having a secondsubcarrier frequency spacing defining the second symbol duration. 25.The OFDM transmitter of claim 24 wherein the OFDM signal generated isassociated with the second OFDM communication protocol, and wherein theinstructions are further configured to cause the transmitter tointerpolate the OFDM signal generated using the base plurality ofsubcarriers to produce an OFDM signal to form the second set of OFDMsymbols.
 26. The OFDM transmitter of claim 20 wherein the second set ofOFDM symbols comprises control data associated with the first OFDMcommunication protocol, the control data being indicative of one of atransmission length, transmission time, transmission type and a channelreservation time associated with at least one of the first and secondset of OFDM symbols.
 27. The OFDM transmitter of claim 26 wherein thecontrol data comprises one of Short Training Field (STF) data, LongTraining Field (LTF) data, Signal Field (SIG) data.
 28. The OFDMtransmitter of claim 20 wherein the second set of OFDM symbols comprisespacket data associated with the second OFDM communication protocol, thepacket data being indicative of one of a transmission length,transmission time, transmission type and a channel reservation timeassociated with at least one of first and the second set of OFDMsymbols.
 29. The OFDM transmitter of claim 28 wherein the packet datacomprises a Clear To Send (CTS) frame having a timer value indicative ofa transmission end time associated with the at least one of the firstand the second set of OFDM symbols.
 30. The OFDM transmitter of claim 18wherein the first and second sets of OFDM symbols are transmitted insequence, as one of contiguous transmissions and non-contiguoustransmissions.
 31. The OFDM transmitter of claim 30 wherein the firstand second sets of OFDM symbols are transmitted as non-contiguoustransmissions separated by a delay and wherein the second set of OFDMsymbols comprises data is indicative of a time for completingtransmission of the first set of OFDM symbols.
 32. The OFDM transmitterof claim 20 wherein the second set of OFDM symbols comprises an OFDMindication indicative of one of an OFDM type, OFDM mode and an OFDMparameter, a symbol duration, a CP duration, a number of subcarriers, asubcarrier spacing, a subcarrier modulation format, and a subcarrierfrequency set associated with the first set of OFDM symbols.